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44-477: It is used for housings where the stiffness of the component is more important than its tensile strength , such as internal combustion engine cylinder blocks , pump housings, valve bodies, electrical boxes, and decorative castings . Grey cast iron's high thermal conductivity and specific heat capacity are often exploited to make cast iron cookware and disc brake rotors. Its former widespread use on brakes in freight trains has been greatly reduced in

88-453: A built up edge . Stainless steel and other materials with a high strain hardening ability also want to form a built up edge. Aluminium alloys, cold worked steels, and free machining steels , as well as materials with a high shear zone don't tend to form built up edges, so these materials would rank as more machinable. The advantage of this method is that it is easily measured with the appropriate equipment. The disadvantage of this criterion

132-502: A device such as the Cutometer. The Cutometer applies a vacuum to the skin and measures the extent to which it can be vertically distended. These measurements are able to distinguish between healthy skin, normal scarring, and pathological scarring, and the method has been applied within clinical and industrial settings to monitor both pathophysiological sequelae, and the effects of treatments on skin. Machinability Machinability

176-479: A graphite microstructure. The silicon promotes good corrosion resistance and increased fluidity when casting. Gray iron is generally considered easy to weld. Compared to the more modern iron alloys, gray iron has a low tensile strength and ductility ; therefore, its impact and shock resistance is almost non-existent. Stiffness Stiffness is the extent to which an object resists deformation in response to an applied force . The complementary concept

220-418: A material attempts to quantify the machinability of various materials. It is expressed as a percentage or a normalized value . The American Iron and Steel Institute (AISI) determined machinability ratings for a wide variety of materials by running turning tests at 180 surface feet per minute (sfpm). It then arbitrarily assigned 160 Brinell B1112 steel a machinability rating of 100%. The machinability rating

264-406: A minimum tensile strength of 20,000 psi (140 MPa). Class 20 has a high carbon equivalent and a ferrite matrix. Higher strength gray irons, up to class 40, have lower carbon equivalents and a pearlite matrix. Gray iron above class 40 requires alloying to provide solid solution strengthening , and heat treating is used to modify the matrix. Class 80 is the highest class available, but it

308-497: A significant engineering challenge. Machinability can be difficult to predict due to the large number of variables involved in the machining process. Two sets of factors are the condition of work materials and the physical properties of work materials. The condition of the work material includes at least eight factors: microstructure , grain size, heat treatment , chemical composition, fabrication, hardness , yield strength , and tensile strength . Physical properties are those of

352-439: A tool to cut through a material is directly related to the power consumed. Therefore, tool forces are often given in units of specific energy. This leads to a rating method where higher specific energies equal lower machinability. The advantage of this method is that outside factors have little effect on the rating. The surface finish is sometimes used to measure the machinability of a material. Soft, ductile materials tend to form

396-415: A variety of chemicals, both metal and non-metal, that can be added to steel to make it easier to cut. These additives may work by lubricating the tool-chip interface, decreasing the shear strength of the material, or increasing the brittleness of the chip. Historically, sulfur and lead have been the most common additives, but bismuth and tin are increasingly popular for environmental reasons. Lead can improve

440-440: Is flexibility or compliance , typically measured in units of metres per newton. In rheology , it may be defined as the ratio of strain to stress , and so take the units of reciprocal stress, for example, 1/ Pa . A body may also have a rotational stiffness, k , {\displaystyle k,} given by k = M θ {\displaystyle k={\frac {M}{\theta }}} where In

484-494: Is flexibility or pliability: the more flexible an object is, the less stiff it is. The stiffness, k , {\displaystyle k,} of a body is a measure of the resistance offered by an elastic body to deformation. For an elastic body with a single degree of freedom (DOF) (for example, stretching or compression of a rod), the stiffness is defined as k = F δ {\displaystyle k={\frac {F}{\delta }}} where, Stiffness

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528-467: Is a parameter of interest that represents its firmness and extensibility, encompassing characteristics such as elasticity, stiffness, and adherence. These factors are of functional significance to patients. This is of significance to patients with traumatic injuries to the skin, whereby the pliability can be reduced due to the formation and replacement of healthy skin tissue by a pathological scar . This can be evaluated both subjectively, or objectively using

572-474: Is determined by measuring the weighted averages of the normal cutting speed, surface finish, and tool life for each material. Note that a material with a machinability rating less than 100% would be more difficult to machine than B1112 and material with a value more than 100% would be easier. Machinability Rating= (Speed of Machining the workpiece giving 60min tool life)/( Speed of machining the standard metal) Machinability ratings can be used in conjunction with

616-482: Is extremely brittle. ASTM A247 is also commonly used to describe the graphite structure. Other ASTM standards that deal with gray iron include ASTM A126 , ASTM A278 , and ASTM A319 . In the automotive industry, the SAE International (SAE) standard SAE J431 is used to designate grades instead of classes. These grades are a measure of the tensile strength-to- Brinell hardness ratio. The variation of

660-458: Is that it is often irrelevant. For instance when making a rough cut, the surface finish is of no importance. Also, finish cuts often require a certain accuracy that naturally achieves a good surface finish. This rating method also doesn't always agree with other methods. For instance titanium alloys would rate well by the surface finish method, low by the tool life method, and intermediate by the power consumption method. The machinability rating of

704-431: Is the ease with which a metal can be cut ( machined ) permitting the removal of the material with a satisfactory finish at low cost. Materials with good machinability ( free machining materials) require little power to cut, can be cut quickly, easily obtain a good finish, and do not cause significant wear on the tooling . Factors that typically improve a material's performance often degrade its machinability, presenting

748-495: Is undesirable, while a low modulus of elasticity is required when flexibility is needed. In biology, the stiffness of the extracellular matrix is important for guiding the migration of cells in a phenomenon called durotaxis . Another application of stiffness finds itself in skin biology. The skin maintains its structure due to its intrinsic tension, contributed to by collagen , an extracellular protein that accounts for approximately 75% of its dry weight. The pliability of skin

792-485: Is usually defined under quasi-static conditions , but sometimes under dynamic loading. In the International System of Units , stiffness is typically measured in newtons per meter ( N / m {\displaystyle N/m} ). In Imperial units, stiffness is typically measured in pounds (lbs) per inch. Generally speaking, deflections (or motions) of an infinitesimal element (which

836-425: Is viewed as a point) in an elastic body can occur along multiple DOF (maximum of six DOF at a point). For example, a point on a horizontal beam can undergo both a vertical displacement and a rotation relative to its undeformed axis. When there are M {\displaystyle M} degrees of freedom a M × M {\displaystyle M\times M} matrix must be used to describe

880-557: The European Union over concerns regarding noise pollution . Deutsche Bahn for example had replaced grey iron brakes on 53,000 of its freight cars (85% of their fleet) with newer, quieter models by 2019—in part to comply with a law that came into force in December 2020. A typical chemical composition to obtain a graphitic microstructure is 2.5 to 4.0% carbon and 1 to 3% silicon by weight. Graphite may occupy 6 to 10% of

924-454: The Taylor tool life equation , V T n = C {\displaystyle VT^{n}=C} , in order to determine cutting speeds or tool life. It is known that B1112 has a tool life of 60 minutes at a cutting speed of 100 sfpm. If a material has a machinability rating of 70%, it can be determined, with the above knowns, that in order to maintain the same tool life (60 minutes)

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968-409: The tensile modulus of elasticity of the various grades is a reflection of the percentage of graphite in the material as such material has neither strength nor stiffness and the space occupied by graphite acts like a void, thereby creating a spongy material. Gray iron is a common engineering alloy because of its relatively low cost and good machinability , which results from the graphite lubricating

1012-502: The SI system, rotational stiffness is typically measured in newton-metres per radian . In the SAE system, rotational stiffness is typically measured in inch- pounds per degree . Further measures of stiffness are derived on a similar basis, including: The elastic modulus of a material is not the same as the stiffness of a component made from that material. Elastic modulus is a property of

1056-425: The addition of sulfur and phosphorus. Aluminium is a much softer metal than steel, and the techniques to improve its machinability usually rely on making it more brittle. Alloys 2007, 2011 and 6020 have very good machinability. Thermoplastics are difficult to machine because they have poor thermal conductivity. This creates heat that builds up in the cutting zone, which degrades the tool life and locally melts

1100-433: The axial stiffness is k = E ⋅ A L {\displaystyle k=E\cdot {\frac {A}{L}}} where Similarly, the torsional stiffness of a straight section is k = G ⋅ J L {\displaystyle k=G\cdot {\frac {J}{L}}} where Note that the torsional stiffness has dimensions [force] * [length] / [angle], so that its SI units are N*m/rad. For

1144-460: The constituent material; stiffness is a property of a structure or component of a structure, and hence it is dependent upon various physical dimensions that describe that component. That is, the modulus is an intensive property of the material; stiffness, on the other hand, is an extensive property of the solid body that is dependent on the material and its shape and boundary conditions. For example, for an element in tension or compression ,

1188-407: The coupling stiffness. It is noted that for a body with multiple DOF, the equation above generally does not apply since the applied force generates not only the deflection along its direction (or degree of freedom) but also those along with other directions. For a body with multiple DOF, to calculate a particular direct-related stiffness (the diagonal terms), the corresponding DOF is left free while

1232-430: The cut and breaking up the chips. It also has good galling and wear resistance because the graphite flakes self-lubricate. The graphite also gives gray iron an excellent damping capacity because it absorbs the energy and converts it into heat. Grey iron cannot be worked (forged, extruded, rolled etc.) even at temperature. Gray iron also experiences less solidification shrinkage than other cast irons that do not form

1276-410: The cutting speed must be 70 sfpm (assuming the same tooling is used). The carbon content of steel greatly affects its machinability. High-carbon steels are difficult to machine because they are strong and because they may contain carbides that abrade the cutting tool. On the other end of the spectrum, low-carbon steels are troublesome because they are too soft. Low-carbon steels are "gummy" and stick to

1320-450: The cutting tool, resulting in a built up edge that shortens tool life. Therefore, steel has the best machinability with medium amounts of carbon, about 0.20%. Chromium, molybdenum and other alloying metals are often added to steel to improve its strength. However, most of these metals also decrease machinability. Inclusions in steel, especially oxides, may abrade the cutting tool. Machinable steel should be free of these oxides. There are

1364-399: The cutting zone. These inclusions are stress risers that weaken the steel, allowing it to deform more easily. Stainless steels have poor machinability compared to regular carbon steel because they are tougher, gummier and tend to work harden very rapidly. Slightly hardening the steel may decrease its gumminess and make it easier to cut. AISI grades 303 and 416 are easier to machine because of

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1408-476: The graphite flakes. Grey iron also has very good damping capacity and hence it is often used as the base for machine tool mountings. In the United States, the most commonly used classification for gray iron is ASTM International standard A48 . This orders gray iron into classes which correspond with its minimum tensile strength in thousands of pounds per square inch (ksi); e.g. class 20 gray iron has

1452-414: The greater the time for the carbon to diffuse and accumulate into graphite. A moderate cooling rate forms a more pearlitic matrix, while a fast cooling rate forms a more ferritic matrix. To achieve a fully ferritic matrix the alloy must be annealed . Rapid cooling partly or completely suppresses graphitization and leads to the formation of cementite , which is called white iron . The graphite takes on

1496-473: The individual material groups, such as the modulus of elasticity , thermal conductivity , thermal expansion , and work hardening . Other important factors are operating conditions, cutting tool material and geometry, and the parameters of the specific machining process being performed. Steels are among the most important and commonly used materials in engineering. Free machining steels are alloys that include elements like sulfur and lead that reduce

1540-555: The machinability for one tool type cannot be compared to another tool type (i.e. HSS tool to a carbide tool). Machinability index ( % ) = cutting speed of material for 20 minute tool life cutting speed of free-cutting steel for 20 minute tool life ∗ 100 {\displaystyle {\text{Machinability index (}}\%{)}={\frac {\text{cutting speed of material for 20 minute tool life}}{\text{cutting speed of free-cutting steel for 20 minute tool life}}}*100} The forces required for

1584-421: The machinability of steel because it acts as an internal lubricant in the cutting zone. Since lead has poor shear strength, it allows the chip to slide more freely past the cutting edge. When it is added in small quantities to steel, it can greatly improve its machinability while not significantly affecting the steel's strength. Sulfur improves the machinability of steel by forming low shear strength inclusions in

1628-465: The measure of how long a tool lasts. This can be useful when comparing materials that have similar properties and power consumptions, but one is more abrasive and thus decreases the tool life. The major downfall with this approach is that tool life is dependent on more than just the material it is machining; other factors include cutting tool material, cutting tool geometry, machine condition, cutting tool clamping, cutting speed, feed, and depth of cut. Also,

1672-496: The plastic. Once the plastic melts, it just flows around the cutting edge instead of being removed by it. Machinability can be improved by using high lubricity coolant and keeping the cutting area free of chip build up. Composites often have the worst machinability because they combine the poor thermal conductivity of a plastic resin with the tough or abrasive qualities of the fiber (glass, carbon etc.) material. The machinability of rubber and other soft materials improves by using

1716-520: The remaining should be constrained. Under such a condition, the above equation can obtain the direct-related stiffness for the degree of unconstrained freedom. The ratios between the reaction forces (or moments) and the produced deflection are the coupling stiffnesses. The elasticity tensor is a generalization that describes all possible stretch and shear parameters. A single spring may intentionally be designed to have variable (non-linear) stiffness throughout its displacement. The inverse of stiffness

1760-432: The shape of a three-dimensional flake. In two dimensions, as a polished surface, the graphite flakes appear as fine lines. The graphite has no appreciable strength, so they can be treated as voids. The tips of the flakes act as preexisting notches at which stresses concentrate and it therefore behaves in a brittle manner. The presence of graphite flakes makes the grey iron easily machinable as they tend to crack easily across

1804-574: The size of chips produced by the machining process. Free machining steels are more expensive than standard steels, but their cost is offset by savings on manufacturing costs. There are many factors affecting machinability, but no widely accepted way to quantify it. Instead, machinability is often assessed on a case-by-case basis, and tests are tailored to the needs of a specific manufacturing process. Common metrics for comparison include tool life, surface finish quality, cutting temperature, tool forces, and power consumption. Machinability can be based on

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1848-408: The special case of unconstrained uniaxial tension or compression, Young's modulus can be thought of as a measure of the stiffness of a structure. The stiffness of a structure is of principal importance in many engineering applications, so the modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is sought when deflection

1892-421: The stiffness at the point. The diagonal terms in the matrix are the direct-related stiffnesses (or simply stiffnesses) along the same degree of freedom and the off-diagonal terms are the coupling stiffnesses between two different degrees of freedom (either at the same or different points) or the same degree of freedom at two different points. In industry, the term influence coefficient is sometimes used to refer to

1936-405: The volume of grey iron. Silicon is important for making grey iron as opposed to white cast iron , because silicon is a graphite stabilizing element in cast iron, which means it helps the alloy produce graphite instead of iron carbides ; at 3% silicon almost no carbon is held in chemical form as iron carbide. Another factor affecting graphitization is the solidification rate; the slower the rate,

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